The present invention is directed to level shifting circuits, and especially to level shifting circuits used for shifting data signals conveying information from a first reference level to a second reference level. Most commonly, the level shifting circuit of the present invention is used to shift data signals from a reference level above ground to a ground reference.
In data communications, it is not uncommon for a manufacturer of a signaling apparatus to specify output signaling to occur relative to a reference level above ground, while downstream apparatuses, especially data transmission apparatuses, require that signaling occur relative to ground for proper operation. There is, therefore, a need for a level shifting apparatus between a data source signal generator and downstream communication apparatuses, such as data transmission apparatuses. As speed of communications (also referred to as speed of operation) for data communication systems has increased, circuitry involved in level shifting operations has had difficulty keeping up. The result has been that level shifting apparatuses have operated as bottlenecks in communication systems and have had the effect of slowing entire systems.
Prior art level shifting circuits have offered unacceptable accuracy because their inability to accommodate power supply voltage variations have resulted in poor control of output signals.
Prior art level shifting circuits have also offered unacceptable accuracy because temperature and process variations in their manufacture have resulted in poor control of output signals.
There is a need for a level shifting circuit that can accommodate power supply voltage variations without sacrificing accuracy of output signals.
There is a need for a level-shifting circuit that can accommodate high speed operations without sacrificing accuracy of output signals.
There is a need for a level-shifting circuit that generates a controlled output signal, even in the presence of temperature and process manufacturing variations.